Semiconductor device manufacturing: process – Gettering of substrate – By layers which are coated – contacted – or diffused
Reexamination Certificate
2000-07-20
2002-07-23
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Gettering of substrate
By layers which are coated, contacted, or diffused
C438S239000, C438S240000, C438S253000, C438S720000, C438S762000, C438S791000
Reexamination Certificate
active
06423617
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to silicon integrated circuit processing, and, more particularly, to a method of forming a semiconductor dielectric in the presence of both gettering and strengthening agents.
2. Description of Related Art
In semiconductor processing, the formation of a gate dielectric typically includes using dry/wet/dry growth techniques to grow an oxide on a substrate surface. In order to form a high quality, low defect gate dielectric, many oxide growth techniques entail using a chlorine source in the process gas flow. In particular, chlorine and other halogens can be introduced to the substrate/oxide interface during oxidation to getter the metallic contaminants that are inadvertently deposited on the wafer surface. Gettering agents, such as chlorine, are used to passivate the metal contaminants and thereby reduce the metal's tendency to attract loose electrons. Alternatively, gettering agents in some cases are used to vaporize the metal contaminants and lift the contaminants off the wafer surface altogether. Without the gettering process, metallic contaminants are known to attract electrons into the dielectric and adversely affect the threshold voltage of the gate structure. As such, gettering of metallic contaminants is essential for the formation of a high quality gate dielectric.
However, the gate dielectric thus formed can still be susceptible to hot electron degradation and dopant penetration which can reduce reliability of the gate dielectric and ultimately cause electrical failures in the device. A hot electron is a high energy charge carrier that is travelling in the channel region of the substrate between the source and drain that is attracted into the gate dielectric and can damage the gate dielectric thereby affecting the performance of the transistor. In particular, a gate dielectric formed of silicon dioxide, for instance, can trap hot electrons via the dangling silicon bonds. The trapped hot electrons have shown to degrade the oxide and erode its insulating properties. Similarly, the gate oxide can also permit dopants such as boron to diffuse into the underlying channel which can alter the threshold voltage of the channel and render the device less reliable.
To address the problems associated with gate dielectric degradation, nitrogen containing compounds are commonly incorporated into the gate oxide to strengthen the lattice structure of the dielectric so as to form a gate dielectric that is resistant to hot electron injection and boron diffusion. This gate dielectric strengthening process is commonly known as gate hardening and is typically performed after gate oxide formation. For instance, the gate hardening process for a gate dielectric that is primarily made of silicon dioxide (SiO
2
) typically comprises subjecting SiO
2
to a gaseous oxy-nitride (N
x
O
y
) to form a silicon oxy-nitride SiO
x
N
y
gate dielectric. The nitrogen improves the lattice structure of the dielectric so that the dielectric is less susceptible to physical damages resulting from dopants or hot electrons. While the nitrogen incorporation process has shown to improve the gate dielectric properties, precise control of the nitrogen profile within the oxide layer is difficult to achieve because the nitrogen distribution largely depends on proper diffusion of the nitridizing species throughout the oxide.
To address this problem, a method has been developed to incorporate nitrogen in situ by bonding nitrogen to silicon and oxygen to form a SiO
x
N
y
dielectric from the outset as opposed to diffusing nitrogen through the dielectric after the formation of SiO
2
. The growth of an in-situ hardened gate oxide typically uses gaseous oxy-nitride N
x
O
y
as a nitrogen source during the oxide growth process whereas the conventional gate hardening process uses N
x
O
y
to diffuse nitrogen into an already formed oxide layer. As a result, the SiO
x
N
y
gate oxide formed using the in-situ method has a more consistent and controlled nitrogen profile. Moreover, the in-situ method incorporates nitrogen into the dielectric at the same time as oxide formation and therefore allows for a reduction in thermal budget and other related processing costs.
Disadvantageously, however, the presence of oxy-nitrides (N
x
O
y
) during gate oxide formation generally precludes the use of chlorine to getter metallic contaminants as chlorine can catalyze an explosive branching chain reaction between N
x
O
y
and O
x
. As a result, gettering of metallic contaminants is usually not performed during the growth of in-situ hardened gate dielectrics because of the above mentioned safety concerns. As a consequence, the quality of the in-situ grown SiO
x
N
y
dielectric is generally inferior when compared to dielectrics that are formed using the conventional dielectric formation process where chlorine can be used during oxide growth to getter metallic contaminants.
Hence from the foregoing, it will be appreciated that there is a need for a method of forming an in-situ hardened dielectric in which chlorine can be safely used to getter metallic contaminants during the formation of the dielectric. Furthermore, it will be appreciated that there is a need for a method of using chlorine and nitrogen simultaneously to getter metallic contaminants and strengthen a dielectric lattice structure without creating a safety hazard. To this end, there is a particular need for a method of forming a nitrogen strengthened SiO
x
N
y
dielectric in which chlorine can be safely used as a gettering agent during the formation of SiO
x
N
y
.
SUMMARY OF INVENTION
The aforementioned needs are satisfied by the present invention which teaches a method of simultaneously strengthening and gettering a semiconductor dielectric. In one aspect, the present invention comprises a process for producing a gaseous gettering agent selected to getter contaminants in the dielectric and a gaseous strengthening agent selected to strengthen the dielectric. In particular, the gaseous strengthening agent is selected to inhibit rapid oxidation of the gaseous strengthening agent by the gettering agent. Furthermore, the process comprises exposing the dielectric to the gaseous gettering agent and the gaseous strengthening agent so as to strengthen the dielectric while simultaneously gettering the dielectric.
In another aspect, the present invention comprises a process for producing a nitrogen strengthened solid dielectric material in a semiconductor substrate. The process comprises producing a gaseous gettering agent and a gaseous nitridizing agent wherein the gaseous nitridizing agent is produced in a form that is not rapidly oxidizable by the gettering agent. Furthermore, the process comprises oxidizing the semiconductor substrate in the presence of the gaseous gettering agent and the gaseous nitridizing agent such that the gettering agent getters the contaminants and the nitridizing agent bonds nitrogen to the oxidized semiconductor substrate during the oxidation to form a dielectric comprising of the oxidized semiconductor substrate material and the bonded nitrogen. In one embodiment, the process can be applied to the formation of a gate dielectric while in another embodiment the process can be used to strengthen the dielectric of a capacitor.
In yet another aspect, the present invention comprises using an H
2
O steam based oxidation system containing dichloroethene (DCE) and ammonia (NH
3
) to form an in-situ hardened SiO
x
N
y
gate dielectric. Preferably, the oxidation system comprises 0.001%-1% by volume dichloroethene (DCE) combined with 0.002%-30% by volume ammonia (NH
3
) in H
2
O steam. Preferably, the percent volume of NH
3
is at least twice the percent volume of DCE. In contrast to other commonly used in-situ gate oxide growth methods that use N
x
O
y
as a nitrogen source, the present invention in this aspect uses a steam based NH
3
and DCE gas stream as a source for both nitrogen and chlorine during the oxide growth process. In particular, a portion of the NH
3
undergoes a gas pha
Elms Richard
Knobbe Martens Olson & Bear LLP
Luu Pho M.
Micro)n Technology, Inc.
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